net/mlx5_core: Introduce access function to modify RSS/LRO params

To be used by the mlx5 Eth driver in following commit.

This is in preparation for netdev "light-weight" open/stop flow
change described in previous commit.

Signed-off-by: Achiad Shochat <achiad@mellanox.com>
Signed-off-by: Amir Vadai <amirv@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>